When Vancouver stay-at-home mom Jasmine Cairo babysits her two-year-old niece Kaia, she does it all: changes diapers, enforces nap time -- even breastfeeds.

Ms. Cairo has a supply of milk, thanks to having given birth to her own 22-month-old, Paris, three months after her twin sister delivered Kaia.

"We didn't really plan it," the 32-year-old says of cross-nursing with her sister Tara. "We had talked about the fact that we'd be nursing at the same time and that 'if my baby needed to nurse, you could nurse him.' "

The wet nurse is back. Like co-sleeping and baby-wearing, cross-nursing is gaining ground among adherents of attachment parenting, a child-rearing style that treats the parent-child bond as sacrosanct. With medical evidence pointing overwhelmingly to the health benefits of breast milk, wet-nursing has also found a niche among women who, for medical reasons, can't nurse.

In a new twist on the age-old practice, many mothers store, freeze and swap breast milk in plastic baggies.

When Toronto mother Janet Belray was diagnosed with breast cancer in her right breast, a mastectomy and chemotherapy ended her six-month-old son's breastfeeding at least a year earlier than she'd intended. A close friend organized six "milk mamas," including one woman Ms. Belray had never met, to pump for baby Julian daily until he was 11 months old. "It was the single most amazing thing these women could have done for me," says Ms. Belray, who celebrated her milk donors at a "weaning" brunch at a Toronto restaurant.

For women lacking their own network of milk donors, Craigslist and eBay postings have popped up hawking breast milk, and at least one non-profit website operates as an online breast-milk swap meet.

In the United States, California-based Prolacta Bioscience sells fortified breast milk to U.S. hospitals for upwards of $100 (U.S.) a day. And in Beverly Hills, clients of Certified Household Staffing can order a wet nurse from the company's website, along with cleaning ladies and nannies.

With demand growing, non-profit human milk banks are now climbing into the North American mainstream to serve babies at risk, including sick and premature infants. In Canada, the only milk bank is the B.C. Women's Milk Bank, connected to the B.C. Women's Hospital. Last year, the bank served 500 recipients, up from only 33 in 1999, and even shipped to Toronto's Sunnybrook Hospital, milk bank director Frances Jones says.

In both Montreal and Toronto, medical teams are working on getting additional banks up and running.

To ensure the safety of banked milk, banks follow guidelines set by the Human Milk Banking Association of North America, including screening milk donors for viruses such as HIV and hepatitis C, and pasteurizing milk to kill any bacteria.

Medical practitioners warn potential milk recipients who rely on their own community-based networks that their babies risk contracting disease. Ms. Belray's doctor told her she should have everyone tested for hepatitis C, but Ms. Belray chose not to test her donors.

Ms. Belray, 42, says she believes the breast-milk mixture that Julian, almost 3, drank along with organic formula boosted his immune system. "He never got sick the whole time."

The sale of breast milk in Canada falls under the scope of the Canadian Food Inspection Agency, but they say it is nearly impossible to monitor. Last summer, Health Canada issued a warning on the risks of shared breast milk in response to an art show in Toronto called the Lactation Station Breast Milk Bar. Visitors to the exhibit were invited to drink the milk of six lactating moms.

As more and more research has mounted to show that breastfed children enjoy lifelong health benefits - they have higher IQs, get sick less, are less likely to be obese and less likely to develop allergies, diabetes and heart disease in later life - pressure has mounted on new mothers to put down the bottle. Recent Statistics Canada figures show 84.5 per cent of mothers initiated breastfeeding in 2003 upon the birth of a baby, up from fewer than 25 per cent in 1965.

Of those who initiate breastfeeding, only 18.7 per cent exclusively breastfeed for six months, while 38.4 per cent breastfeed exclusively for four months. But many of today's mothers were themselves bottle-fed, and some struggle to breastfeed with little support. "We're returning from a culture of bottle-feeding," says Stephanie Knaak, a PhD sociology student at the University of Alberta who is specializing in the topic of breastfeeding. "We're relearning this entire art or practice all over again."

Sharing milk helps to alleviate the feeling of being tied down by a nursing infant, mothers say. Toronto mom Rachel Epstein nursed a friend's baby when his bottle ran out while she was babysitting. "He wanted more," says Ms. Epstein, who was nursing her own one-year-old. "I thought, 'Oh well, I'll nurse him.' I had a supply," she says, adding that her friends were fine with her impromptu decision.

Ms. Cairo in Vancouver says she's learned to love the convenience factor. Wet-nursing means each sister has been able to plan overnight, parents-only getaways while baby has a sleepover with the other sister. "I know lots of parents who, even for years, never go out for dinner," she says. "They never leave the kids."

She says nursing her niece has also confirmed to her the power of bonding through breastfeeding. "I feel like I have another little girl," Ms. Cairo says. "I didn't think nursing her would make that much difference."